- Participant has history of familial long QT interval (the QT interval is the portion of an electrocardiogram (ECG) between the onset of the Q wave and the end of the T wave, representing the total time for ventricular depolarization and repolarization) syndrome or prolonged Bazett-corrected QT interval (QTcB) (males > 470 msec; females >480 msec) at baseline as measured on a 12-lead ECG.